This invention relates generally to circuits for supplying power to arc discharge circuits. More specifically, it relates to improvements in circuits utilizing ballasts as current limiting devices in such circuits.
The art has long known of the use of ballasts in circuits for supplying power to arc discharge devices such as arc furnaces and lamps, including flourescent lamps. An essential electrical characteristic of such devices is the need to provide a high starting or ionization voltage and then a lower voltage sufficient to maintain the arc or current flow. After ionization has been achieved, if the voltage is not reduced then current flow will increase unless it is limited in some way for the device itself exhibits what are referred to as negative resistance properties. If the current is not limited it will increase and unstable operation will result and there may be damage to the device.
The necessary current limiting in arc discharge devices has been provided by arc ballasts. If the power supply is D.C. then the ballast is usually a resistor in series between the device and the source. When the source is A.C. the ballast usually includes a substantial reactance. In either case the ballast is relatively large and costly, constituting a significant percentage of the cost of the circuit. Further, inasmuch as the ballast, in order to serve its purpose, is highly reactive at the supply frequency the circuit is relatively inefficient due to the losses in the ballast.
Therefore, it is an object of this invention to provide a novel power supply circuit for arc discharge devices which is smaller, lighter and, therefore, less costly than ballasts used in the prior art.
It is a further object of this invention to provide a novel power supply circuit for arc discharge devices which is electrically more efficient than those of the prior art.
It is another object of this invention to provide a novel power supply circuit in which the arc current can be controlled to eliminate the ballast, for dimming the light intensity, and for reducing electromagnetic interference of ballasts used in the prior art.
It is another object of this invention to provide a novel power supply circuit which can provide emergency lighting or power by the addition of a battery and simple circuit.
It is another object of this invention to provide a novel power supply circuit which may be made in a number of different physical forms embodied in the novel concepts of the invention.